Tungsten alloys



United States Patent 3,184,304 TUNGSTEN ALLOYS George M. Andes, Wilmington, Del., assignor to E. I. tlu Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Mar. 16, 1961, Ser. No. 96,075 Claims. (Cl. 75-134) This invention relates to high-temperature tungstenbase alloys containing chromium and titanium. These alloys may also contain as optional ingredients small amounts of iron, nickel, or cobalt.

Although tungsten possesses the highest melting point of all the metal elements, it suffers the disadvantage of being very susceptible to oxidation at elevated temperatures. For this reason, the use of tungsten as a hightemperature material has been somewhat limited. The present invention provides tungsten-base alloys having significantly improved oxidation resistance. It will be seen from data presented herein that as much as a 100-fold decrease in the rate of oxidation can be obtained with ternary tungsten-base alloys containing chromium and titanium within certain specified proportions. More specifically, it has ben found that alloys containing about -40% by weight of chromium, about 1-25% by weight of titanium, about 010% by weight of a metal selected from the group consisting of iron, nickel, and cobalt, and combinations thereof, the balance being essentially tungsten in an amount of at least 45% by weight, are particularly resistant to oxidation at temperatures as high as 1200 C. As can be seen from the above ranges, the elements iron, nickel, and cobalt are optional elements which may or may not be present in the alloy composition. The table which appears hereinafter will show that excellent oxidation resistance can be obtained even when these elements are omitted from the alloy. Also, it should be pointed out that the 0-10% range for the iron group metals refers to the total weight of iron, nickel, and cobalt present.

In a preferred embodiment of this invention, the alloys comprise from by weight of chromium, about 1%l3% by weight of titanium, about 0%-10% by weight of metals from the group consisting of iron, nickel, and cobalt, the balance being essentially tungsten in an amount of at least by weight.

Any of several well-known methods may be used to prepare the alloys of this invention. For example, they may be prepared by the arc melting of the metal constituents in powdered form. In preparing the alloys in this fashion, the metal powders are blended in the proper proportions and thoroughly mixed to yield the desired nominal composition. If desired, the mixture of metal powders may be compacted into small billets before are melting. Because of differences in melting points and in vapor pressures of the alloying elements at high temperatures, loss by volatilization or scattering of powders by the arc may thus be minimized. However, the powder mixture can be melted directly without compaction. In order to insure homogeneity of composition in the alloys, the mixture of metals should be melted several times, and preferably the casting turned over between melts.

For a clearer understanding of the invention, the following specific examples are given. These examples are intended to be merely illustrative of the invention and not in limitation thereof.

EXAMPLE I An alloy of tungsten, chromium, and titanium was prepared as follows:

A mixture of metal powders comprising 50 parts of tungsten, 40 parts of chromium, and 10 parts of titanium was thoroughly blended and compacted under a pressure of approximately 50 t.s.i. This compact was then are melted under vacuum and cooled. The casting was turned over and remelted, the melting and cooling process being carried out four times to insure homogeneity in the sample.

The melted sample was analyzed and found to be 50% tungsten, 39% chromium, and 11% titanium by Weight.

The specimen was weighed and placed in a furnace which was a part of a continuously recording thermobalance. A flow of dry air at a rate of 1000 cc./min. was directed over the sample and the specimen was held at a temperature of 1200 C. After five hours in the oxidizing atmosphere, the weight gain on the sample was found to be 5.3 mg./cm. The alloy sample was ex posed to the oxidizing atmosphere at 1200 C. for a total of 42 hours. The initial rate of oxidation of the sample was found to be 2.8 mg./cm. /hr., while the final rate after 42 hours was found to be 0.5 mg./cm. /hr. The oxide film which formed on the sample Was found to be very adherent.

A sample of pure tungsten was tested under the same conditions as the alloy sample. The initial rate of oxidation was found to be 150 mgjcmP/hr. This rate did not diminish by the end of one hour of testing. The weight gain after five hours of oxidation testing was 296 mg./cm.

EXAMPLES II THROUGH VII Other alloys were prepared and tested in the same manner as the alloy of Example I. The composition of these alloys and the results of testing for resistance to oxidation and for rate of oxidation at 1200 C. are given in the following Table I.

Table 1 Alloy composition (analyzed), weight percent Oxidation test results (Recording Thermobalance) in flowing air Total hrs. at Oxidation rate Weight gain, 1200 G. rug/em], W Gr Ti Fe Ni after 5 hours Initial Final unless otherwise specified 5 B 150 296 Bal. 39 42 2.8 b 0. 5 5. 3 Bel. 27. 2 50 5. 7 0. 6 11. 3 Ba]. 38 68 b 0. 2 10 Bal. 27.6 66 10 0. 5 7. 1 B81. 39. 5 138 2. 2 b 0.2 4. 5 132.1. 39. 5 96 1. 0 01 3. 0 Ba]. 39. 5 96 1.8 0.05 2. 5 Bel. 37.3 68 0.2 27 Bill. 35. 6 24 a 253 Alter one hour.

b The oxide scale on these samples was found to be especially adherent.

After 24 hours sions and: flame tips for gas burners.

this invention. One method which has frequently been employed to effect alloying of tungsten with other elements hsa been to prepare. compacts of metal powders and to effect sintering of the compacted powder A sug gested method of compaction of metal powders is one in which the compaction is achieved by the carefully controlled detonation of an explosive charge. This explosive compaction of powder imixes has'been very effectively employed in the preparation of dense compacts which are then sinteredto effect alloying of the elements.

Another method which has been employed in the preparation -of the tungsten-rich alloys of this invention is that of sealing uncompacted powder blends in' stainless steel tubes. These tubes are heated to 1250"" C. and then rolled and forged. This process yields alloy slabs of almost full density. The .alloysystems of this invention are particularly well adapted to thisrolling and forging technique.

considerable solubility for gases,.poros'ity'of the compact;

is minimized. The stainless steel tubes in which the metal powders are heated-may be evacuated to minimize further the porosityof the compact.

The alloys of this invention were-prepared: using commercial metal powders 'of' the highest purity available. Because of the extremely high' melting point of tungsten and the high vapor pressures of chromiumand titanium at the temperatures, under which the alloys. of "this in vention are prepared, itis sometimes difficult to prepare these alloys without lossofsome amount'of one'o r. more of the alloying elements. The claims are therefore to" be construed as; defining the 'alloy compositions fin parts by:

weight as determined by analysis. j

The alloys of this invention are suitableias materials of construction in hot rollsforrollingmills. The alloys can also be used to manufacture furnace parts where strength at high 'temperature'is needed and exposureto air or oxygen may be encountered. Also, the alloys may be fabricated into dies used inhigh-ternperature extru- Since it isobvious that manychanges Since some of the. alloying elements have titanium, 0.1% iron, 8.1

, 2. A high-temperature, oxidation-resistant alloy Iconsisting essentially of; about 20%40.% by weight of chromium, about 1%25% by weight of titanium, the balance being essentially tungsten in an amount of at least 45% by Weight. V V

3. A high-temperature, oxidation-resistant alloy consisting essentially of about%.40% by weight of chro- "mium, about 1%-13% by weight of titanium, and up to 10% by weight of a metal selected from the group consisting of iron, nickel, cobalt, and combinations thereof, the balance being essentially tungsten in an amount'of at least 45% by weight. i

'4. A high-temperature, -oxidation resistant alloy consisting essentially of about 35 %-40% byvweigh t of chromium, about 1%l3% :by. weight: of titanium, the balance being essentiallytungsten in an amount of at least by weight. I V i 1 5. A high-temperature, oxidation-resistant alloy con- .sisting essentially of, by Weight, 39% chromium, 11%

titanium, the balance bjeing' essentially tungsten.

6. A high-temperature, oxidationqesistant alloy consisting essentially of, by weight, 39.5% chromium, 1.6% nickel, the balance being. esfsentiallytungsten. V 1 V i 7. A. high-temperature; oxidation resistant alloy consisting essentially of, by weight, 27.2%. chromium, 12.8

titanium, theibalance being essentially tungsten; I

8.'A high-temperature,. oxidation-resistant alloy'consistingessentially of, by,weight, 37.3% chromium, 1.5%

titanium, 7.8% iron," the balance being essentially tungsten. ,I 1 1 i V i 9.. A;l1igh-temperature, oxidation-resistant alloy consisting essentially *of, by Weight, 27 .6% chromium, 24.5%

V titanium, the balance being essentiallytungsten'.

40, and modifications can be made in the above-described details withoutdepart ing from the nature and s pirit of the invention, it isitobe understood that the invention, is not to be limited to said 7 details except as set forth'in the appended claims? I V .The embodiments of the invention in which an exclusive property or privilege is claimed are defined asfollowsz,

1. A high-temperature, oxidationgresistant 'alloyi consisting essentially of about'20%-40% by weight of chromium, about 1 -25% by weight of titanium, and up to 10% by weight of a metal selected from the group consisting ofiron, nickel, cobalt, and combinations thereof, the balance being essentially tungstenin an amount-of at least 45% by weight.

10. A high-temperature, oxidation-resistant alloy consisting essentially of, by weight, 38% chromium, 10% titanium, the balance being essentially tungsten.

Referehces Cited the Examiner r v 7 UNITED STATES PATENTS V 1,471,326" 10/29 Copland 1755x 2,030,229- 2/ 36 Schwarzkopf 75 176 2,470,790 5/4 Price 75-176 2,491,866 12/49 Kurtz 75-47 2,850,385. 58 Nisbet 75-176 72,977,225 3/61 Wlodek et al. ...a 75-176 7 .FOREIGN PATENTS" 550,648 1 2/57 Canada. [741.360 :13/52 Great Britain.

DAVID L. R K, PrimaryfExaminer. RAY K. WINDI-IAM, Examiner. 

1. A HIGH-TEMPERATURE, OXIDATION-RESISTANT ALLOY CONSISTING ESSENTIALLY OF ABOUT 20%-40% BY WEIGHT OF CHROMIUM ABOUT 1%-25% BY WEIGHT OF TITANIUM, AND UP TO 10% BY WEIGHT OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL, COBALT, AND COMBINATIONS THEREOF, THE BALANCE BEING ESSENTIALLY TUNGSTEN IN AN AMOUNT OF AT LEAST 45% BY WEIGHT. 